The idea of using lasers for controlling machinery is well known in the art. Indeed, in the U.S. Pat. No. 4,807,131 issued to Clegg, a fully automated earth grading system for grading a tract of land is disclosed. The system comprises a power driven earth grading machine which comprises a frame, an earth grading tool, and means for adjusting the earth grading tool relative to the frame. The system additionally includes a laser beam generator remotely located from the earth grading machine for projecting a laser beam in a predetermined pattern relative to the earth to be graded. A detector was carried on the grading machine for receiving the laser beam.
A laser aligned robotic machining system for use in rebuilding heavy machinery is disclosed in the U.S. Pat. No. 5,768,137 issued to Polidoro et al. In this invention a precision positioning system is used for resurfacing and repairing rails and guideways of large, heavy machinery at user's facilities. The precision positioning system comprises several elements including a monorail frame, multiple guides extending along an outer surface of the monorail frame, supports for holding the monorail frame in position, a movable base surrounding the monorail frame and a laser alignment system.
In the U.S. Pat. No. 5,767,479, Kanaoka discloses a laser beam machining apparatus and corresponding method which employs a laser beam to pretreat and machine a workpiece. A laser beam is carried out by irradiating beforehand the laser beam along a final locus for a main machining, under such a condition as to obtain an energy density for forming a groove angled to a surface of a work. Thereafter, the laser beam is irradiated to the groove, while changing only the energy density according to a cutting condition to cut the work.
However, the prior art inventions do not address the following problem. As machines change grade, they quickly move out of the range of the laser, typically (+/-) 1 meter in the vertical direction. If multiple laser systems are set up, they would conflict with each other and be difficult to distinguish one from the other.
What is needed is a multiple laser system combined with a satellite navigational system for controlling grading machine, wherein at each position of the grading machine a single laser is selected to control the vertical coordinate of an implement.